| The patient was admitted to the hospital. The sputum specimen was inoculated to sheep blood agar. Based on the colony morphology seen in the accompanying photograph, the most likely identification is: | View Page |
| The name of the rapid test as illustrated in this photograph, often used to differentiate S. pneumoniae from viridans streptococci, in which a drop of 10% deoxycholate was placed on an area of growth, is: | View Page |
| Middle ear damage in cases of S. pneumoniae infections are caused primarily by: | View Page |
| The bacterial species shown growing on 5% sheep blood agar was recovered from the spun sediment of a midstream urine specimen after 24 hours incubation at 35C. Each of the following tests would be useful in supporting the presumptive identification of Enterococcus species except: | View Page |
| PYR Differential As mentioned before, the spot PYR test is commonly performed to separate Enterococcus species (positive reaction) from the Group D streptococci (S. bovis, S. equinus), which are negative.It should be remembered that Streptococcus pyogenes (group A) also produces PYR; therefore, additional characteristics such as beta hemolysis are important.Some species of Aerococcus and Gemella are also PYR-positive; however, they can be suspected if large cocci in tetrads or clusters are observed on gram stain.These species are rare isolates in most clinical practices. | View Page |
| The spot test that is helpful in separating Enterococcus species (positive as shown in the photograph) from the viridans streptococci and S. pneumoniae (both negative) is: | View Page |
| Enterococcus ID Illustrated in this composite photograph is the gram stain of Enterococcus species (upper), illustrating gram positive cocci arranged in pairs and short chains.The viridans streptococci generally form gram positive cocci in long chains; the gram-positive cells of S. pneumoniae, on the other hand, may appear similar in gram stain.In the lower right is shown a 6.5% NaCl tube. The turbidity indicates growth, a unique characteristic for Enterococcus species.In the lower left frame is a picture of a bile esculin hydrolysis slant, showing a positive reaction (black pigment) characteristic of Enterococcus species. The streptococci are uniformly negative.Some strains of Leuconostoc species and Pediococcus species can grow in 6.5% NaCl and are bile-esculin positive; however, they should be ruled out because of the negative PYR reaction. | View Page |
| Illustrated in the upper photograph are tiny pinpoint 24-hour colonies recovered from one of the splenic abscesses. The wide zones of beta hemolysis are better seen in the close-in view of the 36 hour culture shown in the lower photograph.
Streptococcus milleri (anginosus) can be suspected if one of the following odors is detected: | View Page |
| Most strains of S. milleri (anginosus) carry the F antigen (see photograph). Rare strains that carry the group A antigen can be differentiated from S. pyogenes by which of the following laboratory tests: | View Page |
| Review 1 Piscitelli SC., Shwed J., Schreckenberger P., Danziger LH.
Streptococcus milleri group: renewed interest in an elusive pathogen.
European Journal of Clinical Microbiology & Infectious Diseases.11:491-8, 1992The following review examines the bacteriological characteristics, epidemiology, pathogenicity and antimicrobial susceptibility of the "Streptococcus milleri group". "Streptococcus milleri group" is a term for a large group of streptococci which includes Streptococcus intermedius, Streptococcus constellatus and Streptococcus anginosus.Usually considered commensals, these organisms are often associated with various pyogenic infections including cardiac, intra-abdominal, subcutaneous and central nervous system infections, particularly with the formation of abscesses.Organisms of the "Streptococcus milleri group" are often unrecognized pathogens due to the lack of uniformity in classifications and difficulties in microbiological identification. Penicillin G, cephalosporins, clindamycin and vancomycin all possess activity against these streptococci.Use of agents with poor activity may promote infections with "Streptococcus milleri group" and allow it to exhibit its pathogenicity. An understanding of these organisms may aid in their recognition and proper treatment. | View Page |
| Group A Strep A Disk/SXT In follow up to the previous question, the upper image again illustrates the colonies recovered from the blood culture bottle. The colonies are small, transluscent, gray-yellow, and surrounded by a wide zone of beta hemolysis.The size of the colonies compared to the zones of hemolysis suggests a group A streptococcus.The susceptibility to bacitracin (zone of inhibition around the "A" disk)(lower photograph) is virtually diagnostic of a group A streptococcus.The absence of a zone of inhibition around the SXT disk indicates resitance to sulfamethoxazole/ trimethoprim. SXT resistance is also shared by group B streptococci, which are, however, resistant to bacitracin.The resistance to SXT is used for the primary recovery of groups A and B streptococci from specimens with mixed culture. Their resistance allows them to selectively grow out from contaminating bacteria that are inhibited by this antibiotic. | View Page |
| Beta hemolytic colonies grew from the blood culture bottle after 18 hours incubation (see photograph). The following tests would be helpful in making a preliminary identification: | View Page |
| Thus, in follow-up to the previous discussion, the reaction shown in the photograph establishes the identification of a group A, beta hemolytic streptococcus. | View Page |
| Review 1 Spencer RC.:
Invasive streptococcEuropean Journal of Clinical Microbiology & Infectious Diseases. 14 Suppl. 1:S26-32, 1995.Before the introduction of antibiotics, serious infections caused by Streptococcus pyogenes (Lancefield Group A streptococci) were common. Before World War II, this bacterium was responsible for as many as 50% of postpartum deaths and was the major cause of death in patients with burns. Also common were the sequelae of streptococcal infections-rheumatic fever and post-streptococcal glomerulonephritis.With the use of penicillin, however, Streptococcus pyogenes was believed to be virtually eliminated as a pathogen. The organism was consigned to the history books, but not for long.In the mid-1980s, focal resurgences of rheumatic fever began to be reported from different areas in the USA, such as Salt Lake City, Utah. In such communities, where increases in cases of rheumatic fever had been reported, the serotypes M-1, 3, 5, 6 and 18 were isolated which, on culture, produced characteristic mucoid colonies. At the same time, reports of increases in invasive streptococcal disease began to surface in both the USA and Europe.Two syndromes were described; invasive streptococcal infection, occurring in previously healthy children and adults, commonly associated with septicaemia resulting from a deep focus of infection such as bone or lung; and streptococcal toxic shock syndrome, involving a cutaneous focus, accompanied by necrotizing or bullous soft tissue changes. Septicaemia is rare in streptococcal toxic shock syndrome, but the most characteristic feature is one of rapidly progressing multi-organ failure. A high proportion of the strains of Streptococcus pyogenes associated with this condition are serotype M-1, and fatality rates approaching 50% have been reported. | View Page |
| A major complication of toxic shock syndrome related to group A streptococci, leading to 50% mortality is: | View Page |
| Review 2 Cunningham MW.:
Pathogenesis of group A streptococcal infections.
Clinical Microbiology Reviews. 13):470-511, 2000Group A streptococci are model extracellular gram-positive pathogens responsible for pharyngitis, impetigo, rheumatic fever, and acute glomerulonephritis. A resurgence of invasive streptococcal diseases and rheumatic fever has appeared in outbreaks over the past 10 years, with a predominant M1 serotype as well as others identified with the outbreaks.Emm (M protein) gene sequencing has changed serotyping, and new virulence genes and new virulence regulatory networks have been defined. The emm gene superfamily has expanded to include antiphagocytic molecules and immunoglobulin-binding proteins with common structural features.At least nine superantigens have been characterized, all of which may contribute to toxic streptococcal syndrome. An emerging theme is the dichotomy between skin and throat strains in their epidemiology and genetic makeup. Eleven adhesions have been reported, and surface plasmin-binding proteins have been defined.The strong resistance of the group A streptococcus to phagocytosis is related to factor H and fibrinogen binding by M protein and to disarming complement component C5a by the C5a peptidase. Molecular mimicry appears to play a role in autoimmune mechanisms involved in rheumatic fever, while nephritis strain-associated proteins may lead to immune-mediated acute glomerulonephritis. Vaccine strategies have focused on recombinant M protein and C5a peptidase vaccines, and mucosal vaccine delivery systems are under investigation. | View Page |
| Factors related to the strong resistance of certain strains of group A streptococci to phagocytosis include: | View Page |
| The test(s) which may be performed to establish a presumptive differential identification between group B streptococci and L. monocytogenes is/are: | View Page |